http://store.steampowered.com/livingroom/
Last week Gabe Newell Said Linux Is The Future Of Gaming at LinuxCon. Which was basically followed by the above website.
But I bet all of this is pointing to Half-Life 4 being confirmed! (You can tell because there's 4 circles.) The one that skipped three! And they'll cast Gordon Freeman's voice actor to be Patrick Stewart!
Although if it is a Steam Box (& said Steam Box is an actual PC) I'll probably cancel my PS4 preorder.
Part One: SteamOS Announced
http://store.steampowered.com/livingroom/SteamOS/